A continuously variable transmission has been described in U.S. Pat. No. 3,340,749. This continuously variable transmission is a power split transmission with three driving modes, a belt drive variator transmission and two mechanical power branches. A mechanical power branch can optionally be drivingly connected by clutches with the input shaft. The engaged mechanical branch and the power branch with continuously variable rotational speed of the belt drive transmission are combined to form a planetary transmission acting as compound gear. In another driving mode, both mechanical power branches are drivingly uncoupled by the input shaft and, by one other clutch, the shaft of the secondary bevelled pulley pair of the belt drive transmission is directly connected with the output shaft. The total power is thus transmitted, via the belt drive transmission, to the output shaft.
In transmissions of this kind, when the vehicle is parked, the variator, as a rule, is adjusted in a manner such that in the driving mode of the slowest speeds with limited transmission input rotational speed, the transmission output rotational speed is zero. To start, the clutch of the slowest driving mode is engaged when still inactive. The starting operation occurs by adjusting the variator. Thus the transmission output rotational speed increases in the compound gear. A slight adjustment of the variator results in a clear change of the total gear ratio. Thereby a regulated start becomes extremely difficult. In particular, a careful shunting is hard to control according to automatic control technology. In this range of very low output rotational speeds of the transmission with limited input rotational speeds, the torque on the variator is stronger than the torque on the transmission output. The variator is thus loaded with a very high torque with a stronger torque than in a direct drive, via the variator, without power split.
This difficult adjustability of the transmission when starting and the strong torque load of the variator constitute a considerable disadvantage.
The problem on which the invention is based is to provide a continuously variable transmission in which starting and reversing are easy to regulate and strong torques on the variator are prevented.
This problem is solved with a continuously variable transmission.